Wednesday, August 17, 2011

New feature: How does AutoRamp work in GBTimelapse 3.1?

In the previous blog post, I announced the release of GBTimelapse 3.1, now with a powerful new feature called AutoRamp. In this post, I explain more about AutoRamp, and the technical aspects that make it such a singular, precise and valuable tool for your time-lapse work. AutoRamp is unique to GBTimelapse 3.1, and unlike any other software product on the market.

AutoRamp is designed to dramatically minimize flicker when ambient lighting conditions are in flux. For example, a classic problem when creating high quality time-lapse footage is achieving a smooth lighting transition at sunset. As the sun sets and the sky darkens, your camera reacts by changing exposures in big ⅓ f-stop intervals. Because of this, your time-lapse has a distracting flicker in brightness between frames. AutoRamp solves this and other lighting problems - sunrises, passing cloud cover, shadows and so on - by determining the optimal settings for your camera, and then changing the camera exposure in precise, smooth increments.

When in Program mode, your camera determines the exposure settings at the instant you touch the shutter button, which is bad news for your time-lapse when lighting is changing. AutoRamp uses an advanced algorithm to analyze a brightness history of previously captured images, and determines the optimal exposure settings for the next image. By calculating exposure from an average, AutoRamp stabilizes your time-lapse and protects it from sudden swings in brightness. Also, the software turns control over to you, so you can adjust the sensitivity of AutoRamp’s history stabilization.

If you specify your GPS coordinates, AutoRamp can additionally use knowledge of the sun’s position to reliably follow rapid changes in lighting at sunrise and sunset. With location information, AutoRamp calculates how fast the sun is moving, and can predict how much brighter or darker the next image should be.

AutoRamp stands for Automatic exposure with bulb Ramping. In non-tech speak, that means the software is automatically optimizing exposure in the most precise f-stop intervals your camera will allow. For example, a camera in Program mode changes settings in clunky ⅓ f-stop intervals. It will use certain preset times: 1 second, 1.3 seconds, 1.6, 2, 2.5, 3.2, 4 and so on. In contrast, AutoRamp uses it’s own bulb timer with precision bulb times, and can adjust the camera by 1/1000 f-stop increments: 1.000, 1.001, 1.002. This precision ensures gradual changes in exposure, minimizing flicker.

Below is a sample of what AutoRamp can do. This time-lapse was made using AutoRamp with a Canon 5D Mk II, 16-35mm lens. No flicker removal was used to make this video! The footage shows three different sunsets over Lake Tahoe with the Milky Way appearing in two of them.

In the next post, I’ll be talking more about the different levels of control you have as a user in GBTimelapse 3.1, when you’re working with the AutoRamp feature. Some of you may want to save time with simpler, preset controls, while others may want to tweak every detail for the best possible results in the Expert mode. Stay tuned for updates here on the blog.

When using a 5DMkII, 7D or T3i I use ND filters to keep the bulb time at least 0.4 seconds. These cameras can run as short as 0.1 seconds, but the timing isn't accurate when that short.

Additionally, AutoRamp can switch between Bulb mode and Manual mode on most cameras. You can set a "bulb switch time" to a value greater than the camera model's minimum bulb time (typically 0.1 seconds. When AutoRamp wants a Tv less than that value, it will switch the camera from Bulb to Manual and use one of the preset Tv settings. And, of course, it will switch back to bulb when needed.